1. Field of the Invention
This invention relates to a method for producing formed blanks from thermoplastically workable component mixtures which predominantly contain raw vegetable materials with a starch component and which are put into their final shape by using thermoplastic or duroplastic deformation in an extrusion molding machine.
2. Description of the Prior Art
First experiments to form component mixtures from edible materials which are thermoplastically workable and can be made into formed blanks have been known since early 1950. An example is shown in U.S. Pat. No. 2,645,587. The particular basis here is a lignocellulose material, for example nut shells, straw, rice hulls, corncobs and the like. However, all of such experiments have not been developed beyond the laboratory stage. German Patent Publication DE-A-25 52 126 discloses a thermoplastically workable and water-soluble mold mass, which is also suitable for producing formed blanks. The described component mixtures essentially consist of parts of starch, casein-sodium as well as glycerin and a part of gelatin and lecithin. All of such mixtures are worked in a mixer, a double-cylinder mill or a masticator into a fine-grained mass which is placed into the funnel of an extruder and processed into the desired formed blanks in a thermoplastic extrusion process.
Another solution is taught by PCT Reference WO90/05161. Here, an additive is admixed to essentially native and natural starch to produce a thermoplastically workable starch and the mixture is melted by the addition of heat and mechanical energy. The additive is a substance which lowers the melting temperature of the starch, so that the melting temperature of the starch together with this additive lies below the decomposition temperature of the starch. While the basis of the component mixtures so far described is an inhomogeneous mixture, and this inhomogeneity is maintained, the natural starch is worked into a melted mass by adding additives and heat, which subsequently is further processed in the form of granulates, pills, tablets or powders. This involves a process which requires a relatively large amount of energy and in which a final product, although biodegradable, loses its natural appearance.
Various thermoplastically workable component mixtures for producing service articles, articles for daily use and for packaging, are described in German Patent Publication DE-A-40 27 786. All of such component mixtures essentially consist of vegetable parts kept in their natural state as much as possible and consist of components of starch, glycerin and preservatives, as well as the addition of fillers containing vegetable proteins as binders and possibly dextrins for making the surface shiny. These components are mixed and subsequently directly worked in duroplastic or thermoplastic machines. The results derived from such teachings are extremely different. It is hardly possible to obtain reproducible results from the same composition of the mixture. It is assumed that the compression and heating of the component mixtures in the extruder worm leads to structural changes which are so complex that they can hardly be kept under control.
Of course, it is known from many patent publications, such as French FR-A-2 349 286, U.S. Pat. No. 4,929,163, European EP-A-0 040 406 and U.S. Pat. No. 3,574,632, how to produce cubes of feed in pellet mills. The materials to be worked have a certain similarity with those for producing thermoplastic or duroplastic formed blanks, but this process represents the last change in shape. Certain subsequent processes then only address the improvement of sterility or shelf life.
In contrast thereto it is not know from the prior art that when producing formed blanks or pellets from thermoplastically or duroplastically workable biomasses, another form of producing the granulate, than that in the extruder press, is used prior to shaping in a plastic molding machine. However, this form of processing has proven to be unusable, because the strongly inhomogeneous mixtures result in an intermediate product which has unequal physical properties and in this way leads to results during the final thermoplastic or duroplastic processing into formed blanks, which are not continuously reproducible.